This invention relates to apparatus for molding paraffin scrapers, also known as rod guides, directly onto oil field sucker rods, and more particularly, to apparatus for cleaning a short pre-determined section of the rod prior to the rod receiving a molded rod guide.
An oil well generally comprises a casing, a string of smaller steel tubing inside the casing, a pump at the bottom of the well and a string of steel rods, commonly referred to as sucker rods, within the tubing and extending into the pump for operating the pump. Various devices well known in the art are provided at the top of the well for reciprocating the sucker rod to operate the pump.
The movement of sucker rods through the tubing has given rise to several problems. Crude oil may contain paraffin and other substances which tend to congeal and deposit upon the walls of the tubing restricting the passage of oil. Second, the reciprocation of the sucker rod in the tubing causes bowing of the rod during compression, resulting in tubing contact and premature wear of the interior surface of the tubing. Third, misalignment of the well bore from true vertical may sometimes result in the sucker rod dragging upon one side or another of the tubing causing additional wear.
A common mode of removing paraffin deposits on the tubing, centering the sucker rod during compression, and reducing abrasive wear of the interior surface of the tubing comprises attaching polymer rod guides to various points along the length of the rod. Typically eight but as few as two and as many as twelve guides may be used. For a thorough discussion of rod guide history and technology, reference may be made to U.S. Pat. No. 4,088,185 to Carson, which is hereby incorporated by reference.
In order for a mold in place rod guide to adhere adequately to the surface of a rod, the rod must be clean. Sucker rods, either new or reclaimed, are coated with either rust or a tar-like corrosion inhibitor which must be removed before the molded guide will adhere properly to the metal. In the past, a steel brush was manually abraded against the rod and the guide molded thereon. In addition to being highly labor intensive, this process was undesirable because hand brushing would often leave small areas unclean. The remaining inhibitor coating would intermix with the molten polymer during molding and severely affect the adherence of the guide to the rod.
This manual technique quickly gave way to a sandblasting process, wherein a rod to be cleaned was fed linearly into a sandblasting cleaning station. The stationary rod was radially surrounded by a group of sandblasting nozzles and the nozzles activated in sequence to thoroughly clean all sides of the rod. When this section was complete, the rod was linearly moved through the cleaning station until the next pre-determined cleaning site was reached and the process repeated.
Although effective, this process has several disadvantages. This process is slow because each site is cleaned in series and the cleaning process becomes a severe bottleneck in the molding operation. This disadvantage has become more serious through the years as the trend to more guides per rod has become more pronounced.
Another disadvantage is this process produces large quantities of fine spent blasting sand requiring disposal. The environmentally safe removal of this spent sand is troublesome and expensive.
Yet another disadvantage of this process is the requirement for large volumes of compressed air. If greater numbers of blast nozzles are utilized, much larger compressors would be needed. This substantial increase in capital cost renders the use of multiple sand blasting stations uneconomical. The sophisticated equipment needed to adequately perform the task is very expensive yet prone to rapid wear and mechanical failure due to the ubiquitous presence of blasting sand grit.
Yet another disadvantage is the required use of blasting sand nozzles which yields a "feathered" edge between cleaned and uncleaned rod rather than a sharply defined edge. This means that either more than needed area must be cleaned, which wastes time and effort, or a portion of rod is inadequately cleaned resulting in inadequate adhesion of the guide to the rods.
In the blasting sand cleaning station it is very difficult to adjust the length of rod section to be cleaned and the amount of cleaning required. Modern rod guides vary in design to address the problems of individual wells and as such are not always of a uniform length. Likewise, rods are received in various condition and some require more cleaning than others. Adjustment of the spacing of sandblasting nozzles and their proper sequencing is very time consuming.
Using a conventional sandblasting rod cleaning station it is very difficult to clean a section of the rod very close to the sucker rod joint or "box". Current experience now indicates this location near the joint to be one of the most desirable places to put a rod guide.
In addition to sandblasting apparatus, mechanically similar computer controlled apparatus utilizing chemical solvents has been employed. In addition to many of the above disadvantages associated with sandblasting, solvent blasting systems are very difficult to adjust to accommodate unequal spacing of guides along the rod. Typically a rod has a guide molded on while another site on the same rod is being cleaned. This reduces wasted molding time but impairs flexibility of guide site spacing. Another disadvantage is that the expensive and potentially dangerous solvents used require careful handling to avoid contact with personnel operating the equipment and environmentally unsafe disposal.
These and other disadvantages of the prior art are overcome by the following invention by providing a quickly adjustable, inexpensive apparatus for simultaneously cleaning a plurality of sites in a rod.